Transporter for installation or removal of an offshore platform and a method for removal of an offshore platform

ABSTRACT

A transporter for removing an offshore platform has an oblong structure with a U-shaped cross section, rotatable by ballasting. The transporter is adapted to remove and carry both a jacket and a topsides simultaneously.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/NO98/00230 which has an Internationalfiling date of Aug. 3, 1998, which designated the United States ofAmerica.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a transporter for installation or removal of anoffshore platform comprising a jacket and a topsides supported by thejacket, the topsides comprising one ore more decks. The invention alsoconcerns a method for removal of an offshore platform comprising ajacket and a topsides supported by the jacket.

2. Description of the Prior Art

The installation of offshore platforms is relevant in connection withthe development of oil and gas fields at sea.

The removal of offshore platforms, consisting of a jacket and a topsidessupported by the jacket, is a field which will become more important inthe coming years, with the decommissioning of a number of offshoreplatforms.

Offshore platforms can be removed by being split up into smaller parts,for example by means of cutting torches or blasting, whereupon each ofthese smaller parts can be lifted aboard a barge or a ship andtransported away. Regardless of how the splitting up is carried out,however, the costs associated with the breaking up and subsequenttransport in smaller parts are substantial.

Thus it is a wish to split up a platform which has to be removed intothe fewest possible parts, in which case a natural division is to divideit into topsides and jacket, each of which is removed separately. In thecase of small platforms with low weight this is relatively problem-free,while in the case of large and heavy platforms it entails lifting withextremely large and expensive crane vessels, if it is even possible atall within the scope of what can be implemented in practice.

The applicant's Norwegian patent applications Nos. 973561, 973562 and973563 respectively disclose a method and a transporter for installationor removal of a jacket for an offshore platform, a method and atransporter for installation or removal of an offshore platform topsidesand a transporter for heavy objects at sea. However, these applicationsare only describing relevant methods and equipment for handling parts ofoffshore platforms, such as topsides or jackets. In Norwegian patentapplication No. 965439 (abandoned before published) there has beendecribed a device for such use, comprising a main unit formed by abarge-like structure with adjustable buoyancy, which can be transported,lowered, manouvered and raised in water, characterized in that anauxiliary unit adapted to cooperation with the main unit comprises meansfor releasable connection to the main unit in at least two differentways, and means for controlling the main unit's functions. Thisembodiment is not a part of the priority claimed from theabove-mentioned Norwegian patent applications Nos. 973561, 973562 and973563.

Norwegian patent applications No. 973561, 973562 and 973563 disclosemethods and transporters which together enable removal of an offshoreplatform in a favourable way, by splitting the platform in jacket andtopsides only and remove these two parts separately. The same methodsand transporters may also be used for installation of an offshoreplatform.

SUMMARY OF THE INVENTION

The object of the invention is to provide a transporter for removal orinstallation of an offshore platform comprising a jacket and a topsidessupported by the jacket, the topsides comprising one ore more decks,which transporter shall be able to carry the jacket and the topsidessimultaneously. The object is further to provide a method for removal ofan offshore platform comprising a jacket and a topsides supported by thejacket, using the transporter according to the invention, in whichmethod the removal of the topsides shall be followed by the successiveremoval of the jacket without any need for an intermediate transfer ofthe topsides to a receiver.

The invention is thus an improvement in relation to Norwegian patentapplications Nos. 973561, 973562 and 973563, using the same constructionelements in combination. The invention thus consist of a combinedtransporter comprising features that enables manipulation of both thetopsides and the jacket, and carrying out these simultaneously. Theinvention enables removal of an offshore platform without the use ofcranes. The invention also enables simultaneous movement of the topsidesand the jacket to a receiver, e.g. a construction yard or a quay, usingonly one and the same transporter.

Provided a rotation of the topsides is acceptable prior to installation,a method corresponding to the method according to the invention may beused for installation of an offshore platform, with the steps performedin the reverse order. This is a clear variant of the method according tothe invention, and will not be explained in detail. It should beunderstood, however. that the inventive concept also covers thisalternative.

Further scope of the applicability of the present invention will becomeapparent from the, detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail in association with adescription of specific embodiments, and with reference to the drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and in which:

FIG. 1 is a perspective view of a transporter according to theinvention;

FIGS. 2 and 3 illustrate a removal of a topsides using the transporteraccording to the invention;

FIGS. 4-7 illustrate a removal of a jacket using the transporteraccording to the invention; and

FIG. 8 illustrates a simultaneous transport of a topsides and a jacketusing the transporter according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a transporter 1 for installation or removal of anoffshore platform according to the invention, comprising a longitudinalunderside 3 and a long side 2 arranged on each side of the underside thethree sides together thereby forming an oblong structure with a U-shapedcross section.

Lower longitudinal pontoons 9 are arranged in the corner areas betweenthe underside 3 and the long sides 2, and upper longitudinal pontoons 8are arranged in the long sides' upper sections. Ballasting chambers areprovided in each of the ends of the pontoons 8, 9, which ballastingchambers preferably extend in towards the pontoons' central areas. Crosselements 7, which are also in the form of pontoons, containingballasting chambers, connect the longitudinal pontoons 8, 9.

Together with an open top side, opposite to the underside 3, and twoopen short sides, the oblong structure forms a body with a prismaticenveloping surface. The ballasting chambers are thereby located in thepoints of intersection between edge lines formed by the intersectionsbetween the surfaces of the long sides 2, the underside 3, the open topside and the open short sides, with the result that a ballasting chamberis arranged in each of the prismatic enveloping surface's eight corners.Thus when ballasting/deballasting the transporter it is possible torotate it to the desired position in the sea.

At one end of the transporter the long sides 2 project past theunderside 3, thus forming a recess 11 in the underside, see FIG. 7. Inthe extension of the recess 11 the lower longitudinal pontoons 9 projectpast the long sides 2 in portions 12.

On each side of the recess 11 there are provided abutment portionsadapted to support and lift the topsides of an offshore platform. Theabutment portions illustrated in FIG. 1 are formed by two lifting beamsor brackets 63, which are structurally joined to the long sides 2 of theoblong structure, i. e. the joint between the abutment portions and thelong sides 2 are able to transfer the weight of the topsides from theabutment portions to the long sides. The abutment portions may compriseimpact dampening elements (not shown) for the absorption of impactduring connection and disconnection of the topsides.

The underside 3 comprises means for securing a jacket 17 (see FIG. 7) inbetween the long sides 2 and the underside 3, in a position in which thesides of the jacket are adjacent to the long sides 2 and the underside 3of the transporter. In the embodiment illustrated in FIG. 1 the meansfor securing the jacket consists of a sliding saddle 52 which is movablein the longitudinal direction F of the transporter. Further, theunderside 3 comprises two longitudinal pontoons 24 provided with groovesor rails 58 to carry the sliding saddle 52 and guide its movement. Meansfor securing the jacket, e. g. brackets may also be provided on the longsides.

The means for securing the jacket 17 to the transporter, i.e. thesaddle, may include chains, hooks or clamps which can be bolted to legsor bracing of the jacket. In a simpler design the saddle may be a fixedsaddle, without any ability for sliding, or the saddle may be omitted,the jacket being secured directly to the transporter. A sliding saddleenabling moving the jacket in the transporter's longitudinal directioncan however be useful for optimizing the position of the transporter'scenter of gravity, thus permitting the transporter to be locatedhorizontally in the sea during transport. Another advantage of thesliding saddle is the possibility for transferring the jacket to areceiver, e.g. a quay at a construction site, by moving or sliding thesaddle with the jacket to the receiver, thereby enabling a transfer ofthe jacket without the use of costly cranes.

In addition, not shown, the transporter comprises piping, valves, pumpswith motors and control equipment for performing theballasting/deballasting. The ballasting/deballasting are remotelycontrolled by means of not shown communication equipment. Alternatively,the ballasting/deballasting may be conducted with an umbilical whichcontains both pressurized water for ballasting and pressurized air fordebaflasting, together with pressurized fluid for operation and controlof the valves.

The transporter illustrated in FIG. 1 further comprises permanentlymounted cutting equipment, illustrated schematically in the form of fourboxes 62, for cutting the jacket after it is secured to the slidingsaddle. As illustrated in FIG. 1 the cutting equipment 62 on the leftside of the transporter is arranged closer to the sliding saddle thanthe cutting equipment on the right side, which illustrates that thecutting equipment is laterally adjustable to enable it to be adapted todifferent designs or positions of the jacket.

FIG. 2 shows the transporter 1 lying horizontally in the sea 18,ballasted to a position in which the longitudinal underside 3 is facingdown and the lower longitudinal pontoons 9 are underneath the seasurface. The transporter is located besides a platform comprising ajacket 17 which is standing in a raised position on the seabed 19 andsupports a schematically illustrated topsides 16, which topsides mayinclude one ore more decks.

The transporter in FIG. 2 has been moved into a position underneath theplatform topsides 16, the jacket 17 being contained in the recess 11.The actual movement of the transporter will be conducted by tugs. Thepositioning of the transporter may be carried out by winches which canvary the length of wires between the transporter and the platform jacketor another fixed point.

The transporter is then deballasted and the abutment portions of thetransporter, i. e. the lifting beams or brackets 63 (see FIG. 1), arebrought into contact with lifting areas of the topsides 16, whichlifting areas may be lower support beams of the topsides. The topsidesis then securely attached to the transporter, e.g. by chains or clamps,and the transporter is further deballasted, whereby the topsides 16,supported by the lifting beams 63, is lifted off the jacket 17.

FIG. 3 shows the transporter 1 with the topsides 16 moved away from thejacket 17.

As can be seen from FIGS. 2 and 3, the topsides 16 are located offsetfrom the central region of the transporter, creating an uneven loaddistribution. The horizontal position of the transporter is achieved bydeballasting ballasting chambers in the projecting portions 12 of thelongitudinal pontoons 9, creating buoyancy that counteracts bouncy inthe opposite side of the transporter.

FIGS. 4-7 show a sequence illustrating removal of a platform jacket fromthe seabed by a transporter according to the invention. For the sake ofsimplicity the topsides are not shown in FIGS. 4, 5, 6 or 7. It shouldhowever be understood that the topsides may be secured to thetransporter as discussed with reference to FIGS. 2 and 3 during theremoval of the jacket, which will be discussed below.

FIG. 4 shows the transporter 1 in a process of by means of ballastingbeing rotated, and FIG. 5 shows the transporter after completedrotation, into a position in which its longitudinal direction F isessentially vertical. The transporter is located beside the jacket 17,with the underside 3 of the transporter facing away from an outer side51 of the jacket. The elevation of the topsides 16, if secured to thetransporter, must be above the top of the jacket 17.

FIG. 6 shows the transporter moved into a position in which the jacket17 is located in between the long sides 2 and the underside 3 of thetransporter. The jacket abuts against the transporter's underside, andis securely attached to the transporter, i. e. the sliding saddle, in aposition in which the sides of the jacket are adjacent to the long sides2 and the underside 3 of the transporter.

The jacket 17 is then released from the seabed 19, e. g. by means of thecutting equipment 62 illustrated in FIG. 1. The transporter with thejacket is thereafter rotated to a horizontal position, which isillustrated in FIG. 7, and moved to a receiver, e.g. a quay of aconstruction yard. The transfer to the receiver may be carried out bycranes. The transfer of the jacket may however, as discussed above,preferably be carried out by sliding the saddle with the jacket to thereceiver.

FIGS. 4-7 thus illustrates a method in which the transporter accordingto the invention is used for removal of the jacket 17 and the topsidesin separate operations, which necessitates an intermediate transfer ofthe topsides to a receiver.

FIG. 8 shows the transporter 1 lying horizontally in the sea, carryingsimultaneously both the topsides 16 and the jacket 17, for movement to areceiver. FIGS. 4, 5 and 8 thus illustrates a method in which thetransporter according to the invention is used for removal of a completeoffshore platform comprising a jacket and a topsides, in which methodthe removal of the topsides is followed by the successive removal of thejacket without any intermediate transfer of the topsides to a receiver.

In both cases, whether the topsides is intermediate transferred to areceiver or not, the jacket 17 may be moved relative to the transporter1 in the longitudinal direction F to optimize the position of the centreof gravity, which movement preferably is carried out by sliding thesaddle in the direction F.

Thus by means of the invention a rational and economically advantageousmethod for removal of an offshore platform is provided.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A transporter for installation or removal of anoffshore platform comprising a jacket and a topsides supported by thejacket, the topsides comprising one or more decks, the transporterhaving an oblong ballastable structure which is rotatable across thelongitudinal direction by ballasting, the oblong structure having twolong sides and an intermediate underside that forms a U-shaped crosssection, the underside in one end being provided with a recess which,when the transporter in a ballasted position is lying in the sea withthe underside horizontally down, is adapted to contain a jacket which isstanding in a raised position on the seabed, the transporter furtherhaving abutment portions adapted to support and lift the topsides offthe jacket when the transporter is deballasted, and that the long sidesand/or underside comprises means for securing the jacket in between thelong sides and the underside, in a position in which the sides of thejacket are adjacent to the long side and the underside of thetransporter.
 2. The transporter according to claim 1, wherein theabutment portions are structurally joined to the long sides of theoblong structure.
 3. The transporter according to claim 2, wherein theabutment portions have beams or brackets adapted to abut lifting areasof the topsides.
 4. The transporter according to claim 2, wherein theabutment portions comprise impact dampening elements.
 5. The transporteraccording to claim 1, wherein the means for securing the jacket comprisea saddle and means for securing the sides of the jacket to the saddle.6. The transporter according to claim 1, wherein the means for securingthe jacket comprise a sliding saddle which is movable in thelongitudinal direction of the oblong structure and comprises means forsecuring the jacket.
 7. The transporter according to claim 1, whereinthe long sides and the underside are structurally joined by longitudinalpontoons.
 8. The transporter according to claim 7, wherein thelongitudinal pontoons comprises longitudinally projecting portionsprojecting past the long sides in extension of the recess.
 9. A methodfor removal of an offshore platform comprising a jacket and a topsidessupported by the jacket, using a transporter, the method comprising thefollowing steps: a) the transporter is ballasted to a position in whichan underside is lying horizontally down in the sea, the transporter ismoved underneath the platform topsides into a position in which thejacket is located in a recess, the transporter is deballasted andabutment portions of the transporter are brought into contact withlifting areas of the topsides, the topsides is securely attached to thetransporter, and the transporter is further deballasted, whereby thetopsides is lifted off the jacket, b) the transporter is rotated andraised by deballasting into a position in which its longitudinaldirection is essentially vertical and the elevation of the topsides isabove the top of the jacket, c) the transporter with the topsides ismoved into a position in which the jacket is located in between the longsides and the underside of the transporter, the jacket is securelyattached to the transporter, the jacket is released from the seabed, d)the transporter carrying the topsides and the jacket is moved to areceiver.
 10. The method according to claim 9, wherein during step c) ord) the jacket is moved relative to the transporter in the longitudinaldirection to optimize the position of the center of gravity.
 11. Themethod according to claim 9, comprising the step of using a transporterhaving an oblong ballastable structure which is rotatable across thelongitudinal direction by ballasting, the oblong structure comprises twolong sides and an intermediate underside that forms a U-shaped crosssection, the underside in one end is provided with a recess which, whenthe transporter in a ballasted position is lying in the sea with theunderside horizontally down, is adapted to contain a jacket which isstanding in a raised position on the seabed, the transporter furthercomprises abutment portions adapted to support and lift the topsides offthe jacket when the transporter is deballasted, and the long sidesand/or underside comprise means for securing the jacket in between thelong sides and the underside, in a position in which the sides of thejacket are adjacent to the long sides and the underside of thetransporter.
 12. The method according to claim 9, wherein the step ofthe transporter carrying the topsides and the jacket to the receiver issimultaneously carried out.
 13. The method according to claim 9, whereinthe step of the transporter carrying the topsides and the jacket to thereceiver is sequentially carried out.
 14. The method according to claim13, wherein the topsides is first carried to the receiver and then thejacket is carried to the receiver.
 15. A portion of a disassembledoffshore platform including at least one of a jacket and topsidesproduced in accordance with the steps of claim
 9. 16. A method forremoval of an offshore platform having at least one of a jacket and atopsides supported by the jacket, the method comprising the steps of:using a transporter for the removal; ballasting the transporter to aposition in which an underside is lying horizontally down in the sea;moving the transporter underneath the platform topsides into a positionin which the jacket is located in a recess, deballasting the transporterand the abutment portions of the transporter which are brought intocontact with lifting areas of the topsides, the topsides being securelyattached to the transporter; further deballasting the transporterwhereby the topsides is lifted off the jacket; rotating and raising thetransporter by deballasting into a position in which its longitudinaldirection is essentially vertical and the elevation of the topsides isabove the top of the jacket; and moving the topsides by the transporterto a receiver.
 17. The method according to claim 16, further comprisingthe steps of: moving the transporter into a position in which the jacketis located in between the long sides and the underside of thetransporter; securely attaching the jacket to the transporter, thejacket being released from the seabed; and moving the jacket by thetransporter to a receiver.
 18. The method according to claim 17, whereinthe step of the transporter moving the topsides to the receiver and thestep of the transporter moving the jacket to the receiver aresimultaneously carried out.
 19. The method according to claim 17,wherein the step of the transporter moving the topsides to the receiverand the step of the transporter moving the jacket to the receiver aresequentially carried out.
 20. The method according to claim 19, whereinthe topsides is first moved to the receiver and then the jacket is movedto the receiver.
 21. The method according to claim 16, wherein the stepof using a transporter, includes the step of using a transporter havingan oblong ballastable structure which is rotatable across thelongitudinal direction by ballasting, the oblong structure comprises twolong sides and an intermediate underside that forms a U-shaped crosssection, the underside in one end is provided with a recess which, whenthe transporter in a ballasted position is lying in the sea with theunderside horizontally down, is adapted to contain a jacket which isstanding in a raised position on the seabed, the transporter furthercomprises abutment portions adapted to support and lift the topsides offthe jacket when the transporter is deballasted, and the long sidesand/or underside comprise means for securing the jacket in between thelong sides and the underside, in a position in which the sides of thejacket are adjacent to the long sides and the underside of thetransporter.
 22. The method according to claim 17, wherein the jacket ismoved relative to the transporter in the longitudinal direction tooptimize a position of a center of gravity during at least one of thefollowing steps: the step of moving the transporter into a position inwhich the jacket is located in between the long sides and the undersideof the transporter; and the step of moving the jacket by the transporterto a receiver.
 23. A portion of a disassembled offshore platformincluding at least one of a jacket and topsides produced in accordancewith the steps of claim
 16. 24. A method for removal of an offshoreplatform having at least one of a jacket and a topsides supported by thejacket, the method comprising the steps of: using a transporter for theremoval; moving the transporter into a position in which the jacket islocated in between the long sides and the underside of the transporter;securely attaching the jacket to the transporter, the jacket beingreleased from the seabed; and moving the jacket by the transporter to areceiver, the method further comprising the steps of: ballasting thetransporter to a position in which an underside is lying horizontallydown in the sea; moving the transporter underneath the platform topsidesinto a position in which the jacket is located in a recess, deballastingthe transporter and the abutment portions of the transporter which arebrought into contact with lifting areas of the topsides, the topsidesbeing securely attached to the transporter; further deballasting thetransporter whereby the topsides is lifted off the jacket; rotating andraising the transporter by deballasting into a position in which itslongitudinal direction is essentially vertical and the elevation of thetopsides is above the top of the jacket; and moving the topsides by thetransporter to a receiver.
 25. The method according to claim 24, whereinthe step of the transporter moving the topsides to the receiver and thestep of the transporter moving the jacket to the receiver aresimultaneously carried out.
 26. The method according to claim 24,wherein the step of the transporter moving the topsides to the receiverand the step of the transporter moving the jacket to the receiver aresequentially carried out.
 27. The method according to claim 26, whereinthe topsides is first moved to the receiver and then the jacket is movedto the receiver.
 28. The method according to claim 24, wherein the stepof using a transporter, includes the step of using a transporter havingan oblong ballastable structure which is rotatable across thelongitudinal direction by ballasting, the oblong structure comprises twolong sides and an intermediate underside that forms a U-shaped crosssection, the underside in one end is provided with a recess which, whenthe transporter in a ballasted position is lying in the sea with theunderside horizontally down, is adapted to contain a jacket which isstanding in a raised position on the seabed, the transporter furthercomprises abutment portions adapted to support and lift the topsides offthe jacket when the transporter is deballasted, and the long sidesand/or underside comprise means for securing the jacket in between thelong sides and the underside, in a position in which the sides of thejacket are adjacent to the long sides and the underside of thetransporter.
 29. The method according to claim 24, wherein the jacket ismoved relative to the transporter in the longitudinal direction tooptimize a position of a center of gravity during at least one of thefollowing steps: the step of moving the transporter into a position inwhich the jacket is located in between the long sides and the undersideof the transporter; and the step of moving the jacket by the transporterto a receiver.
 30. A portion of a disassembled offshore platformincluding at least one of a jacket and topsides produced in accordancewith the steps of claim 24.